The present invention relates generally to torque coupling devices, and more particularly to an electromechanical coupling assembly for avoidance and control of rotor overspeed conditions during propeller pitch control operation.
Engine overspeed is a major concern for turboprop engines, particularly during landing maneuvers. During landing, turboprop vehicles often control blade pitch to reverse the angle of attack of propeller blades. If blade pitch reversal is too gradual, propeller blades may be driven by airflow, rather than the reverse, transmitting harmful torque to the turboprop engine. This can erode the propeller blades, and can cause catastrophic damage to the turboprop engine. Most turboprop vehicles reverse blade pitch very quickly to avoid these conditions. Rapid propeller blade pitching poses its own challenges, however, as blades may be briefly unloaded when pitched edgewise into the wind while transitioning to a reverse pitch. This transient unloading of the propeller blades can cause harmful engine rotor overspeeds.
To avoid engine damage from engine shaft overspeeds, many turboprop systems spool engines down during propeller blade pitch reversal and rely on engine overspeed limiters that close fuel supply governor valves and shut down or reduce fuel to engine(s) if engine overspeed conditions are detected. Once spooled down, an engine requires significant time to spool back up. Consequently, the engine may be incapable of producing the required torque and propeller thrust to respond to an aborted landing command in time to regain altitude and avoid ground obstacles.